Most
people think of driveways and sidewalks when concrete is mentioned.
Concrete is also used as a structural building material in many large
buildings around the country. The problem with concrete as a building
material is that as it develops cracks, the material becomes
weaker.

Researchers are currently investigating ways to make
smart materials that can heal themselves from cracks and other minor
imperfections as a way to prolong the life of the material and
increase its strength. A grad student named Michelle Pelletier from
the University of Rhode island has made a discovery that may one day
lead to smart materials that are cost effective to produce and easy
to use.

Pelletier is a master's degree candidate and
has developed
a method of embedding microencapsulated sodium silicate
healing agents directly into concrete. The idea is that the tiny
microcapsules, which hold the sodium silicate agent that reacts with
calcium hydroxide naturally in concrete, will rupture when cracks
form and release the repairing agent.

When the sodium silicate
inside the microcapsules reacts with the calcium hydroxide in the
concrete a chemical reaction causes a gel-like material to form that
can fill cracks and pores in the area of the crack and hardens in
about a week.

"Smart materials usually have an
environmental trigger that causes the healing to occur,"
explained Pelletier, who is collaborating on the project with URI
Chemical Engineering Professor Arijit Bose. "What's special
about our material is that it can have a localized and targeted
release of the healing agent only in the areas that really need
it."

Tests of the self-healing concrete have shown that
when stressed to near breaking the concrete with the
microencapsulated sodium silicate is able to regain up to 26% of its
original strength. Standard concrete when stressed to similar levels
only regains 10% of its strength. Improvements in the

Another
potential benefit of the new self-healing concrete being studied is
if by immediately filling cracks in the concrete, water can be
prevented from reaching the steel reinforcement bars that are used to
add strength to concrete. Water getting to the steel reinforcement
bars causes the bars to rust leading to reduced strength.

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I was under the impression that Expoxy-coated rebar effectively eliminated rebar corrosion in new construction?As far as cure time, it depends on the application and time. Concrete cure time isn't always the critical path. Bridge structural concrete is often given a full 30 day cure.